In a practice it has since ceased, Google used special code to get around Safari's privacy controls, allowing the company to track users on computers and mobile devices. Google has previously told CNET that the company used known functionality in Safari to provide features that Google users had enabled. Further, the advertising cookies generated did not collect personal information, Google added.

The FTC was reportedly looking into whether Google's action violated a 2011 settlement agreement between the agency and the company over privacy concerns related to the launch of Google Buzz. That settlement required Google to "obtain express affirmative consent" from users -- opt-in, in other words -- any time it proposes any "additional sharing" of certain types of user information.

Sanctions for violating the agreement could reach $16,000 a day.

That agreement, in which Google did not admit to any wrongdoing, also mandated regular reports on the company's privacy practices prepared by an independent professional for the next 20 years. Google would eventually close Buzz and replace it with another social-networking experiment called Google+

Google said it could not comment on the specifics of the investigation.

"The FTC is focused on a 2009 help center page published more than two years before our consent decree, and a year before Apple changed its cookie-handling policy. We have now changed that page and taken steps to remove the ad cookies, which collected no personal information, from Apple's browsers," a Google representative told CNET.

CNET also contacted the FTC for comment and will update this report when we learn more.

A Google representative previously defended the company's behavior as "[providing] features that signed-in Google users had enabled. However, the Safari browser contained functionality that then enabled other Google advertising cookies to be set on the browser."

Google has been involved in a number of privacy tussles over the years, the most recent of which involves a revision of its privacy policy to grant it explicit rights to "combine personal information" across multiple products and services.

Last month, a U.K. regulator announced it was reopening its investigation into how the Web giant's Street View program gathered personal data, saying that information provided in an earlier U.K. investigation appeared to have been contradicted by information provided to the Federal Communications Commission. Google responded by denying that it misled the U.K. regulator.